A large number of different measuring methods are known for this purpose such as the NMR measuring technique, microwave methods or capacitive methods. In practice, only a few have found widespread use, some for only the measurement of a single constituent.
Measuring the product moisture of whole grain kernels by means of microwaves is known. However, even more widespread in grain processing is the use of capacitive measurement as disclosed, for instance, in Applicant's commonly owned German reference 30 24 794. The determination of the water content of whole kernels, and also the regulation of the amount of moisturization to a specific water content, can be achieved with great precision by using this capacitive measurement.
Capacitive measurement uses a plate capacitor, that is, via an element of large area. For this purpose, the sample to be measured moves past the capacitor plates, which is ideal for an in-line measurement, that is, for a measurement in the product flow. By appropriate design of the measuring section, average sample values can be established.
A sample preparation is necessary for the on-line measurement of the moisture of flour and semolina using Near Infra-Red (NIR) Reflectance Spectrometer.
NIR measurement requires not only a light source but also an optical system which accordingly functions in the manner of a point measurement. As is known, every movement, be it the optical system or the sample to be measured, creates particular problems for the optical system and can cause the surface character to become unsharp.
This problem is satisfactorily resolved in that the product sample for NIR measurement not only is brought into a constant state, for example, as regards pressure and density, but the product sample is stopped, respectively, that is, it is arrested for the actual measurement such as in a laboratory measurement. The Applicant was able to introduce a corresponding measuring device (see European Patent Application No. 179 108) into practice with remarkable results. However, as a great drawback, it was found that the measurement of whole kernels, for instance, the protein content of whole grain kernels, is not possible with this process. In practice, this lead to the following measuring situation:
the water content of the whole kernel is determined by the capacitive measuring technique or, if need be, the microwave measuring technique, PA1 the protein content of flour is measured with the above described NIR method, PA1 the protein content of whole kernels must, however, be determined in the laboratory. PA1 the product is conveyed in front of an NIR measurement recorder as a compact stream PA1 the wavelength range or ranges of the reflected light from a larger number of individual measurements are detected, the individual measurements being performed one after the other in time, and each individual measurement being performed for an entire spectrum of a moving sample with measuring times below 100, preferably below 50, milliseconds for a spectrum PA1 and the constituents are determined by statistical averaging of the relevant measurements and calculated on the basis of a calibration value.
Furthermore, many on-line, special measuring devices, for example, for product color, are currently available for intermediate mill products. However, in every case, a calibration with a calibrating specimen must be performed to be able to correct all interfering parameters.
Particularly disturbing, however, is the fact that 3 to 5 fundamentally different wavelength ranges, from gamma rays to microwaves, are used in one and the same production plant such as a mill. Thus, the measurement results frequently can be compared only with great difficulty even though the product, such as whole kernels, semolina or flour, is basically the same.
It is an object of the invention to eliminate at least a substantial portion of the described drawbacks and to make possible an in-line measurement without the requirement of sample removal from the production flow.